Engines may include crankcase ventilation systems to vent gases out of the crankcase and into an engine intake manifold to provide continual evacuation of gases from inside the crankcase in order to reduce degradation of various engine components in the crankcase. During certain conditions, crankcase ventilation systems may be monitored to identify breaches in the system. For example, a fresh air hose (breather tube) may become disconnected, an oil cap may be off or loose, a dipstick may be out, and/or other seals in the crankcase ventilation system may be broken resulting in degradation of various components included in the crankcase.
Various approaches may be used to monitor crankcase ventilation system integrity. For example, diagnostic blow-by approaches may be used wherein a pressure sensor used in the crankcase and a valve in a PCV fresh air hose are opened and a breach in the system is determined based on resulting changes in crankcase pressure or vacuum. Other approaches may use a combination of pressure sensors positioned at different locations in the crankcase ventilation system to monitor crankcase ventilation system integrity.
However, the inventors herein have recognized potential issues with such approaches. As one example, they may add additional hardware, such as additional sensors and valves, to the monitoring system, thereby increasing costs and complexity. As another example, based on the location of the sensor, some combinations of pressure sensors may read substantially the same pressure under certain conditions, leading to an increase in redundancy without an increase in the accuracy of the diagnostic routine. As still another example, even with the use of multiple sensors, a location of the breach may not be accurately discerned. For example, breaches caused by a breather tube becoming disconnected may not be properly distinguished from breaches caused by an oil cap coming off. As such, without knowing the location and nature of the breach, an appropriate mitigating action may not be performed.
In one approach, to at least partially address these issues, a method for an engine is provided. The method comprises, indicating a location of crankcase ventilation system breach based on each of a transient dip in crankcase vent tube pressure during cranking and a change in crankcase vent tube pressure during steady-state engine airflow. In this way, a location and nature of the breach may be better determined and an appropriate mitigating action may be accordingly chosen.
In one example, an engine crankcase ventilation system may include a crankcase vent tube coupled between an air intake passage and a crankcase. Specifically, the vent tube may be mechanically coupled to the air intake passage at a first side and mechanically coupled to the crankcase at a second, opposite side. A pressure sensor (or flow sensor) may be positioned within the crankcase vent tube for providing an estimate of flow or pressure of air flowing through the vent tube. During engine cranking, before fuel is injected into any engine cylinder and while an air flow through the vent tube and into the intake manifold is low, a transient dip in pressure may be sensed by the crankcase vent tube pressure sensor. In response to an amplitude of the transient dip being smaller than a threshold (e.g., a substantially negligible transient dip in crankcase vent tube pressure), a controller may infer that flow through the vent tube is disrupted due to a breach in the integrity of the crankcase ventilation system. For example, the controller may infer that the crankcase vent tube may have gotten disconnected. The controller may also monitor a change in vent tube vacuum relative to a change in steady-state manifold air flow after engine cranking, when engine speeds are above a threshold (e.g., at or above idle) and while manifold air flow is higher than a threshold. For example, in response to vent tube vacuum generation not being proportional to an increase in manifold air flow during engine running, crankcase ventilation system degradation may be confirmed.
The controller may further discern whether the crankcase vent tube is disconnected at the first side or the second side based on each of the amplitude of the transient dip (e.g., relative to a threshold) as well as the change in steady-state vent tube pressure relative to the change in steady-state manifold air flow after engine cranking. As one example, in response to the amplitude of the transient drip being lower than a threshold amplitude and substantially no vent tube vacuum generated during higher engine manifold air flow conditions, the controller may infer that the crankcase system breach is at the first side due to disconnection of the vent tube from the air intake passage at the first side. As another example, in response to the amplitude of the transient drip being lower than the threshold amplitude and reduced vent tube vacuum generated during the higher engine manifold air flow conditions, the controller may infer that the crankcase system breach is at the second side due to one of disconnection of the vent tube from the crankcase at the first side, detachment of the oil fill port cap, detachment of the crankcase oil level dipstick, or blockage of the vent tube at the second side. The controller may further distinguish between the breaches at the second side based on an estimated orifice size of the breach. For example, a large orifice size may indicate that the breach is due to detachment of the oil fill port. Based on the location of crankcase integrity breach, the controller may perform an appropriate mitigating action. For example, the controller may set an appropriate diagnostic code while also limiting engine speed or load so as to delay depletion of lubricant from the breached crankcase and aspiration of lubricant from the crankcase into engine components.
In this way, crankcase vent tube pressure characteristics may be monitored during cranking and after cranking to better identify crankcase ventilation system breaches, and to better distinguish breaches in the ventilation system at the air intake passage side from those at the crankcase side. By using an existing sensor to identify a location of crankcase system degradation, the number of sensors and valves employed in a crankcase ventilation monitoring system may potentially be reduced, providing cost and complexity reduction benefits. Further, the approach allows the crankcase ventilation system to remain active during a diagnostic procedure.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.